Here's one of my absolute favourite footnotes, concerning King Murune of Lancre, who met a terrible fate:

"Involving a red hot poker, a privy, ten pounds of live eels, a three mile stretch of frozen river, a butt of wine, a couple of tulip bulbs, a number of poisoned eardrops, an oyster and a large man with a mallet. King Murune didn't make friends easily."

'Why d'yer think I want it opened?''Er... why?' said the Lecturer in Recent Runes.'To see why they wanted it shut, of course.' **This exchange contains almost all you need to know about human civilization. At least, those bits of it that are now under the sea, fenced off or still smoking.

I Believe that bit is concerning the Bathroom designed by B.S Johnson?

I love the footnotes.
They make me feel like the author is talking directly to me, I think it's quite an intimate way of writing. CS Lewis creates a similar effect by directly addressing the reader in an informal way.
I think the footnotes make (for me, anyway) the books better than any TV/film adaptation could ever be.

… I read him his rites, whereupon, he said up, yours copper. Sgnt Detritus then, cautioned him, upon which he said, ouch…

One of my favourite footnotes:
*This at least was true. Rincewind could scream for mercy in niniteen languages, and just scream# in another forty-four.#This is important. Inexperienced travellers might think that 'Aargh!' is universal, but in Betrobi it means 'highly enjoyable' and in Howondaland it means, variously' I would like to eat your foot', Your wife is a big hippo' and 'Hello, Thinks Mr Purple Cat.' One particular tribe has a fearsome reputation for cruelty merely because prisoners appear, to them, to be shouting 'Quick! Extra boiling oil!'